Slenderness ratio calculations uses wrong radius of gyration

[Anonymous]

Hi All,

I'm facing a problem in the design verification of structural steel columns in Robot 2019 and was wondering if someone had a solution?

My design follows AISC, and when performing the slenderness check, Robot switches between the correct radii of gyration values (ry and rz). For instance looking at the first image, the circled column is a UC 356x406x467. The radii of gyration should be: ry = 10.7cm and rz = 17.5 cm as per the orientation of the column, however they are reversed in the calculations (image 2) and hence I keep getting an instability error.

Was wondering if someone faced a similar issue before and if they found a fix for it?

I noticed the same issue in the forum question below:

https://forums.autodesk.com/t5/robot-structural-analysis-forum/slenderness-value-in-steel-design/m-p...

But the solution is for robot 2013 and i'm currently using Robot 2019. 

Thank you.

[Krzysztof_Wasik · Accepted solution]

Hi @Anonymous 

In Robot Structural Analysis 

Iy, Ly,ry ...parameters refer to plane parallel to I section web  

Iz, Lz,rz...parameters refer to plane parallel to I section flange plane

Looking at your structure screenshot, I think that buckling length coefficients are defined not correctly for selected column ( Ky should be >than Kz )

I have checked manually slenderness and radius of gyration values and they seem to be correctly calculated

[hasan.icat]

Hello, friend gave an answer, but I found a site online that you can verify. You can verify your calculation here. (link to calculation)